This invention relates in general to apparatus and processes for fabricating flexible belts and more specifically to apparatus and processes for fabricating flexible electrophotographic imaging belts.
Various techniques have been devised to form belts from webs. Thermoplastic webs may be joined by overlapping the edge of one web over another and placing the overlapped or seam portion of the webs over a base beneath an ultrasonic vibrating welding element. The technique of ultrasonic welding of thermoplastic material is well known and illustrated, for example, in U.S. Pat. No. 4,532,166, U.S. Pat. No. 3,879,256, U.S. Pat. No. 3,939,033, U.S. Pat. No. 3,947,307 and U.S. Pat. No. 3,459,610, all of these patents being incorporated herein by reference in their entirety.
Unfortunately, batch processes for cutting and welding webs into belts require considerable time, duplicate manual handling, occupy excessive floor space and also require extensive equipment for alignment, cutting, welding trimming and other processing steps. Also, excessive manual handling increases the likelihood of damage to sensitive substrates or coatings, particularly for coated substrates that must meet precise tolerance requirements such as flexible electrostatographic imaging members including photoreceptors for high speed electrostatographic copiers, duplicators, printers and the like. Scratches and even fingerprints on the vulnerable surfaces of a sensitive, flexible photoreceptor renders the photoreceptor unacceptable for most electrostatographic copiers, duplicators and printers.
Also, when multiply batch handling techniques are utilized to fabricate belts, it is also often difficult to achieve uniform belt conicity and uniform quality. Moreover, because of differences in belt size requirements for different electrostatographic copiers, duplicators, printers and the like, a machine suitable for fabricating a belt of one diameter or width cannot be readily used to prepare a belt of a different diameter or width without encountering delays and expense. Further, lap joints formed with the leading edge over the trailing edge cannot be readily changed with the trailing edge over the leading edge for new batches where one side of a belt differs from the other side.
Automatic systems for fabricating belts have been created that overcome many of the problems encountered with manual or multiple batch belt making techniques. For example, automatic systems are described in U.S. Pat. No. 4,838,964 and U.S. Pat. No. 4,878,985. both of these patents being incorporated herein by reference in their entirety. A typical process involves providing a flexible web having a leading edge, horizontally conveying the leading edge of the flexible web from a supply roll to a predetermined distance past a slitting station, slitting the web at the slitting station to form a trailing edge of a web segment having the leading edge at one end and the trailing edge at the opposite end, gripping only the leading edge and trailing edge while supporting the web segment adjacent the leading edge with at least one upwardly directed fluid stream, conveying the leading edge toward the trailing edge to allow gravity to form a downwardly hanging U-shaped loop in the web segment between the leading edge and trailing edge as the leading edge is conveyed toward the trailing edge, inverting the leading edge and the trailing edge of the web segment, overlapping the leading edge and the trailing edge of the web segment and permanently securing the leading edge to the trailing edge to form a belt.
Although many good belts may be fabricated with this system, it has been found that many belts produced by this system can contact underlying support surfaces such as a belt forming table during cutting of the web into segments, forming the segment into a loop, overlapping opposite ends of each segment, and welding the overlapped ends of each segment. Contact between the web and or belt and the belt forming table can damage the belt or web and increase friction that can inhibit acceptable formation of the loop thereby resulting in a defective belt. To prevent contact of the region of the belt between its ends, an attempt has been made to support the web over the belt forming table by means of a plurality of small air nozzles in the belt forming table. These nozzles supply a layer of air between the photoreceptor material and the belt forming table surface. The photoreceptor web floats on this layer of air. This reduces friction between the photoreceptor material and the belt forming table. When the web is floating properly, the force of gravity is adequate to pull the photoreceptor material down between two spaced apart gripping members utilized to form the belt loop. However, problems with the this belt forming technique are encountered in varying degrees, depending on the direction and amount of curl inherent in the photoreceptor web being used to form the belt. When the photoreceptor web possesses positive curl, the material presents a concave cross sectional shape to the surface of the belt forming table with the top of the dome of the concave shape facing upwardly, e.g.; having a shape similar to the cross section of an open umbrella. This concave shape captures the cushion of air between the material and the belt forming table and allows the material to easily float above the belt forming table. This is a desirable condition. With the material floating on a cushion of air, the force of gravity is usually sufficient to pull the web segment material down between the two gripping members as the leading edge is conveyed toward the trailing edge of the web segment. When the web has no curl, the material presents a flat shape to the surface of the belt forming table. This flat shape reduces the ability of the web to float because the volume of air produced by the small air nozzles in the belt forming table cannot maintain an adequate air cushion under the web. This causes the web to occasionally touch the surface of the belt forming table thereby increasing friction between the photoreceptor web and the belt forming table. When this condition occurs, the force of gravity may not be strong enough to overcome the force of friction acting on the web, and the web segment fails to fully drop down between the two gripping members as the leading edge is conveyed toward the trailing edge of the web segment. This failure of the web segment to fully drop and assume a "U" shape causes intermittent jamming of the web segment in the belt fabricating machine and loss of belt products. When the web possesses negative curl, the material presents a convex shape to the surface of the belt forming table with the bottom of the dome of the convex shape facing downwardly, e.g. having a shallow "U" shape. The convex shape does not allow a cushion of air to build up under the photoreceptor web and greatly reduces the ability of the web to float. This allows the web material to come into direct contact with the belt forming table thereby increasing friction between the table and the web. With this excess friction, the force of gravity is not sufficient to pull the web segment down between the two gripping members as the leading edge is conveyed toward the trailing edge of the web segment. Poor belt quality can adversely affect electrophotographic imaging performance, particularly in high performance monochrome and color copiers, duplicators and printers which demand precise tolerances throughout the belt. Poorly formed belts, scratches and other blemishes on belt surfaces can be readily detected with the naked eye and are of unacceptable quality. Scrapping of poor quality electrophotographic imaging belts can significantly affect manufacturing yields.